1. Field of the Invention
The present invention relates to a leadless chip inductor for use in various electronic devices, and also to a method of producing such a chip inductor.
2. Description of the Related Art
In recent years, there is a trend for reduction in the sizes of electronic devices, as a result of progress in the technology for the production of various electronic parts including semiconductors in the form of leadless chips.
On the other hand, the requirement for higher relaibility of these leadless chip parts is becoming more senere due to current progress in related technologies such as high-density packaging, reflow brazing and so forth, as well as diversification of function of the electronic devices.
A typical conventional chip inductor will be explained hereinunder with reference to the drawings.
Referring first to FIG. 1 which is a transparent perspective view of a chip inductor, a coil element is constituted by winding a coil 12 on a magnetic core 11 such as a drum-shaped core. This coil element is fixed to the upper surfaces of a pair of metallic terminal plates 13. Coil lead lines 14 are connected mechanically and electrically to the upper surfaces of the metallic terminal plates 13 by brazing or welding as at 15. A molded cover encloses a major part of the metallic terminal plates 13 including the connections 15 and coil element. The portions of the metallic terminal plates 13 outside the molded cover are suitably shaped by, for example, bending in conformity with the manner of packaging of the electronic devices on which the chip inductor is to be mounted.
The chip inductor having the described construction exhibits superior electric characteristics because the influence of the metallic terminal plates 13 on the magnetic field produced by the coil core 11 is reduced. On the other hand, however, this chip inductor suffers a problem that the position of the electric and mechanical connection between the coil lead lines 14 and the upper surfaces of the metallic terminal plates 13 are fluctuated undesirably, with a result that the reliability of the connection is impaired particularly when the chip inductor is mass-produced. This problem will be explained in more detail with reference to FIG. 2.
FIG. 2 illustrates the manner in which coil lead lines 14 are connected to the metallic terminal plates 13. The coil lead lines 14 led from the coil 12 on the coil core 11 are wound around fixing pins 17 provided on a coil winding device or a coil winding jig. Numeral 18 designate electrodes for electrically and mechanically connecting the coil lead lines 14 to the metallic terminal plate 13. In operation, after the ends of the coil lead lines 14 are wound around the fixing pins 17, the connecting electrodes 18 are pressed onto the metallic terminal plates 13 through the intermediary of the coil lead lines 14. During the pressing, the fixing pins 17 are allowed to move so as to slack the coil lead lines 14, in order to avoid cutting of the coil lead lines 14. The connection is conducted by brazing or welding.
The number of turns of the coil winding, as well as the kind of the wire material, has to be changed to meet various demands for coil performance and characteristics. Namely, the specifications of the chip inductor vary depending on uses and other factors. This inconveniently causes a variation in the positions from which the coil lead lines 14 are led from the coil 12. In addition, the coil lead lines 14 have to be slacked during pressing as explained before. This results in fluctuation or variation of the positions at which the coil lead lines 14 are connected to the metallic terminal plates.
Another problem encountered with the conventional chip inductor is that breakaway of the coil lead lines 14 tends to occur at portions where the lines are connected to the metallic terminal plates, when a tension is applied to the lead lines which are laid along the surfaces of the metallic terminal plates. This is attributable to the fact that the stress is concentrated to a sole point on each coil lead line 14 where it is connected to the metallic electrode plate.